Covering devices of this type which comprise a metal support plate, resting on appropriate bearing walls or purlins, this plate being associated on top and towards the outside of the premises thus covered, with a layer of insulating material having a suitable thickness and with a waterproof external lining in the form of sheets, covering the insulating layer, are already known. However, in the conventional solutions, in order to withstand the effects of compression or tearing which are exerted on the assembly, as a result of wind in particular, it is essential to join the metal plate and the external lining which trap the insulating layer between them, using mechanical connection means, such as screws, rivets, bolts or the like, which pass through the metal plate in order to interact with an appropriate fastening member such as nuts, washers, counter-rivets, clips or the like, ensuring a suitable and safe locking of the elements thus joined.
In general, these solutions require the sheet, usually made of a bituminous material forming the water-proofing lining, to be pierced for the passage of the fixing bolt or screw whose head rests on a metal washer bearing on the external surface of this lining, this screw then passing through the insulating layer and finally the support plate so as to ensure screwing on its protruding extremity. Notably, and in the most common way, these solutions do not require a tapping hole to be made for the passage of the fixing screws in the plate, these screws usually being of the "Parker" screw type, which are well known in the art.
However, it may then be desirable to cover the assembly with a second waterproofing sheet extending either over the whole surface of the lining, or only at the site of the screw heads, the lining sheet or sheets being applied over the insulating layer which, preferably, is formed of juxtaposed panels, resting against the supporting metal plate. As a variant, a first sheet of the insulating lining may be unrolled dry over the insulating panels and fixed to the plate by means of through screws as described above, and the external waterproof lining may then be adhesively bonded or welded, if need be while protecting the underlying insulating panels from the heat, or the fixing screws may also be installed at the location where the various sheet widths forming this lining overlap, the edge of each width being adhesively bonded or welded on the border of the edge of the adjacent width, covering the metal bearing washers of the screw heads.
In all cases, the fixing screws, rivets or bolts pass in principle through the plate and require the latter to be pierced, which constitutes a drawback. To overcome this, it is possible to envisage, either ensuring the essential mechanical connection by making anchoring grooves and ribs in the external face of the plate, which has for example a dovetail-shaped profile for bolt heads whose threaded end, which protrudes outwards after passing through the insulating layer, interacts with appropriate locking components, which constitutes a costly and impractical solution which complicates in particular the installation and assembly of the roof covering, or alternatively welding these bolts directly to the external face of the plate against which the insulating panels bear.
However, in either of these solutions, either as a result of the piercing of the plate, or because of the welding of the bolt or of the means for immobilizing the latter, the other face of the plate which constitutes the ceiling of the covered premises is impaired, the holes leaving unattractive markings, whereas the welding of the bolts introduces burn marks, which is unacceptable, particular if the corresponding surface of the plate has been prelacquered.
It is therefore essential to install an added false ceiling under the plate, which is once again a costly solution and requires considerable labour time for its installation and fixing.